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THE BIG BANG
HOW HAS OUR UNDERSTANDING
OF THE UNIVERSE EVOLVED?
UNIT 2
THE BIG BANG
CONTENTS
UNIT 2 BASICS
3 Unit 2 Overview
4 Unit 2 Learning Outcomes
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6
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Unit 2 Lessons
Unit 2 Key Concepts
Looking Back: What Happened in Unit 1?
KEY CONTENT
10 Threshold 1: The Big Bang
12 How Did Our View of the Universe
Change?
13 Ptolemy, Brahe, Copernicus, and Galileo
14 Newton, Leavitt, and Hubble
15 What Emerged From the Big Bang?
16 Looking Ahead: What’s Next in Unit 3?
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UNIT 2
OVERVIEW
Key Disciplines:
Physics and astronomy
Timespan:
Roughly 13.7 – 13.5 billion years ago
Key Question:
How has our understanding of the Universe evolved?
Threshold for this Unit:
Threshold 1: The Big Bang
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UNIT 2
LEARNING OUTCOMES
By the end of Unit 2, students should be able to:
1. Use the big history themes of collective learning and claim testers to explain how and why our
understanding of the Universe has changed over time.
2. Explain the basics of the Big Bang theory and the primary evidence that supports this theory.
3. Use texts to develop an explanation or argument about why scientists changed their minds
about the nature of the Universe, and use claim testers and collective learning to support their
explanation or argument.
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UNIT 2
LESSONS
2.0 The story starts!
The Big Bang is where big history begins. Everything that’s ever existed – including you – traces
back to this unimaginably profound event.
2.1 How did our view of the Universe change?
Does the Sun revolve around the Earth? Wait – that doesn’t sound right. Astronomers have used
the tools of their time to understand the Universe, each generation building on the theories of the
one before them.
2.2 What emerged from the Big Bang?
Out of the chaos of the Big Bang came the first atoms, the building blocks of every single thing.
2.3 Ways of knowing: The Big Bang
Astrophysicists and cosmologists use specialized methods to study the Big Bang and our Universe.
The questions they ask haven’t really changed, but the ways they look for answers… that’s another
story.
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UNIT 2
KEY CONCEPTS
• authority
• intuition
• Big Bang
• logic
• claim testers
• Universe
• evidence
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LOOKING BACK
WHAT HAPPENED
IN UNIT 1?
Unit 1 introduced the Big History course and shared four main themes: thresholds of
increasing complexity, scale, collective learning, and claim testing.
• Big history is a modern, scientific origin story told by a global community.
• Big history tells the 13.7 billion year story of the Universe.
• Thresholds of complexity are a foundation of big history: they’re fragile, diverse, precise, and
they led to entirely new things in the Universe.
• Big history is so big that in order to talk about it, we need to use measurements on an entirely
different scale from the ones we use everyday.
• Claim testing helps us assess the trustworthiness of information.
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KEY CONTENT
HOW DID OUR VIEW OF
THE UNIVERSE CHANGE?
Main Talk / David Christian
• The ancient Greek thinker Ptolemy proposed a view of the Universe which was dominant in
Europe for more than 1,000 years.
• Ptolemy’s Universe consisted of six planets, a Moon, and a Sun that moved in circular orbits
around the Earth.
• Over time, human observations of the planets and stars became more precise and led some
scientists to suggest alternative theories.
• Copernicus, Kepler, and Galileo contributed to a new view which put the Sun at the center of
the Universe, with the Earth moving around it in an elliptical (rather than a circular) orbit.
• In the 20th century, Hubble measured the distance and speed of many galaxies and found that
most were moving away from Earth. He determined that the Universe was extremely large and
was still expanding.
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PTOLEMY, BRAHE,
COPERNICUS, AND GALILEO
Articles / Cynthia Stokes Brown
In this set of articles, Cynthia Stokes Brown provides biographies of key figures who contributed to
our changing view of the Universe.
• Ptolemy created the view of the Universe that dominated European thought for over 1,000 years.
• Tyco Brahe is considered the last great naked-eye astronomer.
• Copernicus was troubled by inconsistencies in Ptolemy’s work and believed that putting the Sun
at the center of the Universe resolved many of these problems.
• Galileo used a telescope to observe the surface of the Moon, the moons of Jupiter, the phases
of Venus, and sunspots. His observations provided important evidence for Copernicus’ idea of a
sun-centered universe.
Continues next slide
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NEWTON, LEAVITT
AND HUBBLE
Articles / Cynthia Stokes Brown
Continued from previous slide
• Isaac Newton was one of the inventors of calculus and did important work in many areas. His
view that the Universe was both infinitely big and infinitely old was very influential.
• Henrietta Leavitt found a way to use Cepheid variable stars to measure the distance to distant
galaxies, which was a method later used by Hubble and others.
• Edwin Hubble discovered a relationship between the distance of galaxies from the Earth and the
speed at which they were moving. His work lead directly to the idea of an expanding Universe.
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WHAT EMERGED FROM
THE BIG BANG?
Main Talk / David Christian
• Hubble’s work showed that the Universe was expanding, which implied that there was a point in
time when the expansion must have begun.
• The idea that the Universe had its origins in a single point is called the Big Bang theory. The best
evidence suggests that the Big Bang occurred 13.7 billion years ago.
• Initially, temperature and pressure in the Universe were so high that matter and energy were an
interchangeable blur. As the Universe cooled and became less dense, the basic forms of matter
and the four fundamental forces also appeared.
• 380,000 years after the Big Bang, the Universe cooled sufficiently for protons and electrons to
join up, forming atoms.
• Once atoms formed, photons began moving, which caused the Universe to light up.
• Scientists have observed remnants of this light, which is called the cosmic microwave
background (CMB). For many scientists, CMB is evidence that provides clear support for the Big
Bang theory.
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LOOKING AHEAD
WHAT’S NEXT?
In Unit 3, the first stars will appear. We will learn:
•
How stars formed
•
About the life (and death) of a star
•
About the origin of heavy chemical elements in aging and dying stars
•
How views of chemical elements changed over time
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